|By Brendan O'Brien and Alex Dobuzinskis

|By Brendan O'Brien and Alex Dobuzinskis

|By Brendan O'Brien and Alex Dobuzinskis

(Reuters) - Federal authorities on Saturday were seeking to learn what drove an airline worker to steal an empty airplane from Seattle's airport in a security scare that caused the scrambling of U.S. fighter jets and ended when the plane crashed.

A Horizon Air ground service agent got into a Bombardier Q400 turboprop aircraft on Friday night in a maintenance area at Seattle-Tacoma International Airport and took off, Horizon sister carrier Alaska Airlines <ALK.N> said.

He flew for about one hour, often erratically with attempts at aerial stunts, before crashing onto sparsely populated Ketron Island in Puget Sound, some 25 miles (40 km) to the southwest.

The 29-year-old man, who has not been officially identified, was suicidal and appeared to have acted alone, according to authorities. He was believed to have been killed in the crash.

Relatives and co-workers identified the man as Richard Russell of Sumner, Washington, who also went by the name Beebo.

"He was a faithful husband, a loving son, and a good friend," the Russell family said in a statement.

"This is a complete shock to us. We are devastated by these events and Jesus is truly the only one holding this family together right now," the family said.

Russell was not known to have had a pilot's license, Horizon Air Chief Executive Gary Beck said at a news conference, and it was not clear how he was able to take off and fly as he did.

"There were some maneuvers that were done that were incredible maneuvers with the aircraft," Beck said. "Commercial aircraft are complex machines. They're not as easy to fly as, say, a Cessna 150, so I don't know how he achieved the experience that he did," Beck said.

The local sheriff's department said on Twitter that either doing stunts "or lack of flying skills" caused the crash.

In partial recordings of Russell's conversations with air traffic controllers that were published online by Broadcastify.com, he said he was sorry to disappoint people who cared about him and described himself as a "broken guy."

"Got a few screws loose, I guess," Russell is heard saying in the recording. "Never really knew it until now."

He also admired the sunset, complained of lightheadedness, and asked whether he would go to prison if he landed safely.

He had worked for Horizon Air for 3-1/2 years and had clearance to tow planes, Alaska Airlines Chief Executive Brad Tilden said at the news conference.

Tilden said airplanes of that type do not have doors that lock or ignition keys like cars.

"The setup in aviation in America is we secure the airfield and then we have the mindset that we have employees that are credentialed and authorized to be there," Tilden said, adding that the airline was working with authorities to investigate.

The FBI is leading the probe, which also includes the Federal Aviation Administration and the National Transportation Safety Board.

"We are going to be thorough, which means taking the time needed to scour the area, delve into the background of the individual believed responsible, and review every aspect of this incident with all appropriate public & private partners," the FBI said in a statement.

Two F-15 fighter jets took to the air from a base in Portland, Oregon, and were on the scene within minutes. The jets were armed but did not open fire, North American Aerospace Defense Command spokesman Cameron Hillier said by phone.

Instead, the F-15 pilots and air traffic controllers tried to guide the plane west, away from populated areas, said Hillier. No one was hurt on the ground, authorities said.

It was unclear how the employee was able to taxi the plane on a runway and take off without authorization.

The Bombardier Q400 turboprop is designed for short-distance flights and can seat 76 passengers, Alaska Air said.